Flowmeters of the variable area type are well known. Such variable area flowmeters are basically tubes which are internally tapered with the larger diameter at the top. A member termed a float with an outer diameter slightly less than the operational minimum diameter of the tube is placed inside the tube and any clearance between the float and the tube forms an annular orifice. The tube is connected into a fluid line so that flow is from bottom to top and the float will move upwardly and be supported at a position where the orifice is just large enough to pass the fluid flowing through the system.
By making the tube transparent so that the float position can be seen through the tube, and by providing a scale alongside, one may read the float position in terms of numbers on the scale. These scale numbers may be of two types. The first is of an arbitrary nature which, by itself, means nothing but becomes meaningful when compared with a calibration curve; the second can be precalibrated for direct reading to show the actual flow volume in given units (for example, cubic feet per minute, or cubic centimeters per minute, etc.) of the fluid for which the meter is calibrated.
At the present time, flowmeters of the type described are readily available from several manufacturers. They are usually purchased calibrated for a particular gas of known specific gravity and calibrated in flow rates at atmospheric pressure. For example, a flowmeter calibrated for air, which has a specific gravity of 1.0, is calibrated in standard cubic feet per hour (scfh) where scfh indicates a flow rate at one atmosphere at 72.degree. Fahrenheit.
Flowmeters used for gases of different specific gravities and/or at different pressures require flow rate conversions based on equations of perfect gas laws. These conversions can be somewhat tedious and error prone. At the present time, there are no known flowmeters available which provide direct reading flow rates for gases of various densities and/or pressures.
Accordingly, the present invention provides a new and improved flowmeter which is so arranged that it may provide direct reading flow rates for various densities and/or pressures.
Another object of this invention is to provide a new and improved flowmeter where the scale indicia may be programmed in accordance with the pressure and specific gravity of the fluid to be tested.
A further object of this invention is to provide an improved flowmeter of the type described where the scale indicia of the flowmeter are represented by selectively programmmed electrically illuminated cells in accordance with the specific gravity and the pressure of the fluid to be tested.